Double insulated electrically powered hand tool and coupler therefor

ABSTRACT

A coupler for drivably connecting the armature shaft and the spindle of a double insulated electrically powered hand tool. The coupler comprises a rigid body formed from an electrically nonconductive material having a blind bore formed at each end thereof to provide an integral annular collar which is dimensioned to slidably receive respectively an axial end portion of the armature shaft and spindle. At least one recess is provided in each bore extending axially inwardly of the body from the base of each bore, each such recess being dimensioned to receive a terminal complementary portion formed respectively on the armature shaft and spindle configured to fit within such recess. A double insulated electrically powered hand tool incorporates the coupler within a bearing block adapted for securement within the casing of the tool, the bearings for the armature shaft and spindle being slidably mounted within the bearing block to secure the coupler in place.

United States Patent [1 1 Pew [ DOUBLE INSULATED ELECTRICALLY POWERED HAND TOOL AND COUPLER THEREFOR [75] Inventor: John P. Pew, Greenville, SC, [73] Assignee: The Singer Company, New York,

69/11, 27 NM; 403/300, 305; l73/163; 308/20, 189, 236, 199, 200

[56] References Cited UNITED STATES PATENTS 3,075,632 1/1963 Watt 64/11 R X 3,221,193 11/1965 Kober 310/90 3,242,998 3/1966 Gubbins 310/50 X 3,399,736 9/1968 Allen et a1 1 173/163 3,423,957 1/1969 Palmer 64/11 R X 3,457,438 7/1969 Badcock 310/50 3,759,336 9/1973 Marcovitz et a1 173/163 Mar. 25, 1975 Primary Examiner-Donovan F. Duggan Attorney, Agent, or Firm-Chester A. Williams, Jr.; Marshall J. Breen; Harold Weinstein [57] ABSTRACT A coupler for drivably connecting the armature shaft and the spindle of a double insulated electrically powered hand tool. The coupler comprises a rigid body formed from an electrically non-conductive material having a blind bore formed at each end thereof to pro vide an integral annular collar which is dimensioned to slidably receive respectively an axial end portion of the armature shaft and spindle. At least one recess is provided in each bore extending axially inwardly of the body from the base of each bore, each such recess being dimensioned to receive a terminal complementary portion formed respectively on the armature shaft and spindle configured to fit within such recess. A double insulated electrically powered hand tool incorporates the coupler within a bearing block adapted for securement within the casing of the tool, the bearings for the armature shaft and spindle being slidably mounted within the bearing block to secure the coupler in place.

1 Claim, 4 Drawing Figures DOUBLE INSULATED ELECTRICALLY POWERED HAND TOOL AND COUPLER THEREFOR BACKGROUND OF THE INVENTION The invention relates to double insulated electrically powered hand tools and more particularly to such tools by which the armature shaft and the spindle are drivably coupled by means of a dielectric coupler element which provides a secondary system of insulation known as protecting insulation. Such protecting insulation is in addition to and independent of the functional insulation of the power tool.

In the present specification the term double insulated power tool or appliance means that in addition to the basic functional insulation necessary for the proper functioning ofthe tool or appliance there is provided a secondary system of insulation designated generally as protecting insulationv The protecting insulation denotes an independent insulation, provided, in addition to the functional insulation, to insure against electric shock to the operator of the power tool in case of failure of the functional insulation. In the protecting insulation an enclosure of insulating material may form a part or the whole of the protecting insulation. In other words, the term double insulation denotes an insulation system comprised of functional insulation and protecting' insulation, with the two insulations physically separate and so arranged that they are not simulta neously subjected to the same deteriorating influences to the same degree. The invention is especially useful when embodied in a power tool such as a grinder, which operates at high speed.

It has been known heretofore to couple the armature shaft of an electrically powered hand tool to the working spindle by means of a coupling element which itself may be made of insulating material. One such prior art construction utilizes as the coupling element a cylindrically shaped member having mutually displaced radial slots at each end. Such slots are dimensioned to accommodate tongue-shaped projections formed respectively at the ends of the armature shaft and working spindle. The radial slots permit both axial and radial play of the tongue-shaped projections, the radial play being limited by rings which surround the slotted portions of the coupling element. Such coupling constructions are, however, susceptible to vibration, particularly when employed in a high speed tool, and varying degrees of chattering result frequently due to improper or unstable alignment of the armature shaft and working spindle. Further, the susceptibility to vibration results in undue wear of the mating portions of the coupler and shaft ends with consequent increased vibration and abbreviated longevity for either the coupling element, armature shaft and/or working spindle. Such parts must then either be remachined or replaced.

SUMMARY OF THE INVENTION It is one object of the present invention to provide a coupler for a double insulated electrically powered hand tool such as a grinder capable of drivably coupling the armature shaft and spindle so as to enable operation of the tool with reduced vibration.

lt is another object of this invention to provide a coupler for a double insulated electrically powered hand tool capable of drivably coupling the armature shaft and spindle and operating with enhanced longevity.

A further object of the invention is the provision of a double insulated electrically powered hand tool in which the armature shaft and working spindle are cou pled in a manner which assures enhanced alignment of such elements.

It is yet another object of this invention to provide a double insulated electrically powered hand tool having a coupler therein which enables operation of the tool at high speed with reduced vibration and with increased service life for the coupler.

Still another object of the invention is the provision of a double insulated electrically powered hand tool in which the coupling of the armature shaft to the working spindle has'bcen made easier, more economical and the assembled coupling made more reliable.

A further object of the invention is to provide a coupler which is provided with an integrally formed collar adapted to clamp the main section of the armature shaft and working spindle to insure an enhanced coupling of such elements.

Other objects and advantages of the invention will become readily apparent from the following descrip tion of the invention.

According to the present invention there is provided a coupler for drivably connecting the armature shaft and the spindle of a double insulated electrically powered hand tool, comprising:

a. a rigid body formed from an electrically nonconductive material;

b. said body having an axially-extending bore formed in each end thereof to provide an integral annular collar which is dimensioned to slidably receive respectively one axial end portion of said armature shaft and spindle; and

c. said body being provided within each of said bores with at least one recess which extends from the base of each bore axially inwardly of the said body, each said recess being dimensioned to receive a terminal complementary portion formed respectively on said armature shaft and spindle configured to fit within said recesses.

According to the present invention there is also provided in a double insulated electrically powered hand tool having an armature shaft connected drivably by means of a coupler to a spindle, the improvement which comprises:

a. a bearing block formed from an electrically, nonconductive material having a first axial end opening dimensioned to slidably receive a first bearing assembly supportive of said armature shaft, a second axial end opening dimensioned to slidably receive a second bearing assembly supportive of said spindle and a central opening in axial communication with said first and second axial end openings dimensioned to enclose in spaced relation a coupler for said armature shaft and spindle; and

b. a coupler positioned within said central opening of said bearing block and comprising a rigid body formed from an electrically non-conductive material, the body of said coupler having an axiallyextending' bore formed in each end thereof dimensioned and configured to slidably receive respectively one axial end portion of said armature shaft and spindle, said body being provided within each of said bores with at least one recess which extends from the base of each bore axially inwardly of the said body, each said recess being dimensioned to receive a terminal complementary portion formed respectively on said armature shaft and spindle configured to fit within said recess.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully comprehended it will now be described, by way of example, with reference to the accompanying drawing in which:

FIG. I is a side view of a double insulated electrically powered hand tool embodying the invention;

FIG. 2 is a view similar to FIG. 1, on an enlarged scale, with part of the tool housing broken away to show the coupler in place therewithin;

FIG. 3 is a sectional view of the coupler and bearing block taken along line 3-3 of FIG. 2; and

FIG. 4 is an exploded perspective view showing the interrelationship between the armature shaft and spindle and the coupler and bearing block with the latter two elements in section.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing, particularly FIGS. 1 and 2 thereof, there is shown a double insulated electrically powered hand tool in the form of a variable speed hand grinder. It will, of course, be understood that the grinder is but one typical example of a double insulated power tool or appliance to which the present invention is applicable. The tool has a housing or casing 12 which may be formed of a dielectric material or of metal. The functional insulation for the tool can take various forms, as is well known in the art, depending upon whether the housing is made of a plastic or dielectric material or made of metal.

The housing 12 includes a rearward section 14 for mounting a motor M having an armature shaft 16 which carries a .fan 18 thereon, all of such elements being shown in phantom. The housing 12 also includes a forward section 20 within which is mounted a bearing block 22. Armature shaft 16 extends into such forward section of the housing and is supported rotatably by hearing 24 at one end of the bearing block. The terminal portion of the armature shaft is-givcn a configuration. such as shown in FIG. 4, whereby it is insertable into a complementary recessed portion 26a of a coupler element 28 to be described hereinafter. The housing section 14 is also provided with an electrical switch 30 for connecting the motor to a source of electric power by means of electric wire 32.

Mounted rotatably also within the forward section 20 of housing 12 is the work spindle 34 of the tool. As with the axial end portion of the armature shaft 16, the terminal portion of the spindle is shaped and dimensioned to fit within a recess 26b provided in the opposite end of coupler 28 from recess 26a. Bearing 36 supports the end of the spindle within the bearing block 22 in the same manner that the end of the armature shaft is supported within the opposite end of the bearing block. Spindle 34 extends through the front and end of housing section 20 and is customarily provided with a collet 38 for securing the working tool element (not shown) to the spindle for rotation. In the case of a hand grinder a grinding wheel would be fitted to the end of the spindle and locked in place by the collet.

As shown most clearly in FIGS. 3 and 4, a rigid coupler element 28 is preferably formed as a cylindrical member. It should be made from an electrically nonconductive material so as to present a dielectric barrier to any possible transmission of electric potential to the spindle in the event of a breakdown of the functional insulation in the motor portion of the tool. The coupler comprises a body 40 having axially extending integral annular collars 42, 44 formed in each end thereof. The collars are given a dimension which will slidably receive axial end portions 46, 48 respectively on the armature shaft 16 and spindle 34. The coupler is also provided with recesses 26a, 26b, as aforesaid, formed in each end which extend from the base of each bore axiallyinwardly of the body 40. Each such recess is dimensioned to receive a terminal portion 54, 56 formed respectively on the armature shaft and spindle which is configured to fit within such recess. In its preferred form, as shown in FIGS. 2, 3 and 4, the terminal portion on each of the armature shaft and spindle is a tabshaped extension and the recess in each end of the coupler is a radial slot which preferably extends substantially the diameter of the bore. The slots, and thus the complementary formed portions on the armature shaft and spindle, are preferably angularly displaced from each other, and a displacement of substantially 90 has been found effective. It will also be noted that preferably each bore is a blind bore rather than one which extends axially completely through the coupler. Thus barrier 57 of solid dielectric material extends between the bases of recesses 26a and 26h. By providing such a dielectric barrier in the coupler rather than a through aperture it is possible to prevent the transmission of any line or motor current through the coupling.

It will thus be seen that upon assembly of the armature shaft 16 and spindle 34 with coupler 28 the terminal portions of the shaft and spindle repose within the recesses 26a, 26b while the axial end portions 46, 48 of the shaft and spindle are slidably supported within the collars 42, 44. Such combined support of the end portions of the armature shaft and spindle within the recesses and collar portions of the coupler is considered to be of importance inassuring stability of the coupling and a consequent reduction in vibration. By this construction the alignment of the armature shaft and spindle has been considerably improved. The resultant coupling is given an enhanced resistance against misalignment of the shaft and spindle during operation of the tool.

The armature shaft 16 and the spindle 34 are provided respectively with bearings 24, 36 which may be force fit onto the ends of said shaft and spindle. The bearings are slidably received within the opposed ends of bearing block 22. Preferably, to facilitate assembly and to maintain proper seating of the bearings within the bearing block, the block 22 is formed with a body portion 58 having axial end openings 60, 62 formed at each end and with a central opening 64 therebetween. The diameter of each of such axial end openings is greater than that of said central opening. Thereby, the internal annular shoulders 66, 68 are formed which serve to limit the axial penetration of bearings 24, 36 into the bearing block. The exterior surface of the bearing block is provided with an upstanding circumferentially extending collar 70 having at least one cut-out 72 therein adapted to receive fastening means such as screw 74 which is threadedly engaged within an aperture 76 provided in forward housing section 20. When the bearing block 22 is so mounted on the housing of the tool it will be observed that the coupler 28, the armature shaft 16, and spindle 34 are free to rotate within the bearing block. Bearing block 22, as is coupler 28, is made of a material which is not electrically conductive. By providing this additional dielectric barrier there is no possibility of live or motor current circumventing the coupler to follow a path around same to the working spindle and thence to the operator through his contact with the forward section of the housing which, in the preferred form of the invention is constructed of metal.

From the foregoing it will be appreciated that a double insulated electrically powered hand tool has been provided by which the armature shaft has been drivably connected to the working spindle by means of a cou- 7 proved. Provision of the integral annular collars at the opposed ends of the coupler for support of the axial end portions of the armature shaft and working spindle respectively is considered, as stated previously, to contribute in a substantial way to stability of the coupled elements as well as the maintenance of proper alignment between such elements.

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present invention relates to a preferred embodiment of the invention which is for purposes of illustration only and is not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.

Having thus set forth the nature of the invention, what is claimed herein is:

l. A coupler assembly for a double insulated electrically powered hand grinder comprising:

a. a housing having a motor portion and a spindle portion interconnected to the motor portion, b. the motor portion being made of dielectric material, c. a motor mounted in the motor portion, d. a metal armature shaft having its forward end tabshaped and extending into the spindle portion,

e. the spindle portion being made of metal and having a substantially hollow rear section joined by a necked-down forward section adapted to be hand held,

f. a rigid hollow bearing block disposed in and connected to the spindle portion at the rear section thereof,

g. the bearing block being made of dielectric material,

h. a metal bearing journaling the tab-shaped end of the armature shaft within the bearing block,

i. a metal spindle disposed in the spindle portion and having its forward end journaled in and extending outwardly from the necked-down section,

j. the spindle having a tab-shaped rear end extending into the bearing block in the direction of and facing the tab-shaped end of the armature shaft,

k. a metal bearing journaling the tab-shaped end of the spindle within the bearing block,

I. a rigid coupler member disposed in spaced relationship to and within the hollow bearing block to interconnect the tab-shaped ends of the spindle and armature shaft in driving engagement with each other,

m. the coupler member being made of dielectric material,

n. the coupler member formed with a cylindrical periphery and having recesses extending inwardly from either end to be separated from each other by an axial barrier formed integrally with the coupler member,

0. each of the recesses is shaped to correspond to the respective tab-shaped end of the spindle and armature shaft to provide a tight engagement therebetween,

p. a short annular securing collar is integrally formed on the coupler member to extend outwardly from the recess on either side thereof, an axial distance less than one-half the axial depth of each of the recesses, and

q. the collars having an internal diameter substantially equal to the outer diameter of the respective spindle and armature shaft which engages the same to form a tight fit between the coupler member and the respective spindle and armature shaft whereby assembly and disassembly is made by a snap-like positive engagement or disengagement therebe- 

1. A coupler assembly for a double insulated electrically powered hand grinder comprising: a. a housing having a motor portion and a spindle portion interconnected to the motor portion, b. the motor portion being made of dielectric material, c. a motor mounted in the motor portion, d. a metal armature shaft having its forward end tab-shaped and extending into the spindle portion, e. the spindle portion being made of metal and having a substantially hollow rear section joined by a necked-down forward section adapted to be hand held, f. a rigid hollow bearing block disposed in and connected to the spindle portion at the rear section thereof, g. the bearing block being made of dielectric material, h. a metal bearing journaling the tab-shaped end of the armature shaft within the bearing block, i. a metal spindle disposed in the spindle portion and having its forward end journaled in and extending outwardly from the necked-down section, j. the spindle having a tab-shaped rear end extending into the bearing block in the direction of and facing the tab-shaped end of the armature shaft, k. a metal bearing journaling the tab-shaped end of the spindle within the bearing block, l. a rigid coupler member disposed in spaced relationship to and within the hollow bearing block to interconnect the tab-shaped ends of the spindle and armature shaft in driving engagement with each other, m. the coupler member being made of dielectric material, n. the coupler member formed with a cylindrical periphery and having recesses extending inwardly from either end to be separated from each other by an axial barrier formed integrally with the coupler member, o. each of the recesses is shaped to correspond to the respective tab-shaped end of the spindle and armature shaft to provide a tight engagement therebetween, p. a short annular securing collar is integrally formed on the coupler member to extend outwardly from the recess on either side thereof, an axial distance less than one-half the axial depth of each of the recesses, and q. the collars having an internal diameter substantially equal to the outer diameter of the respective spindle and armature shaft which engages the same to form a tight fit between the coupler member and the respective spindle and armature shaft whereby assembly and disassembly is made by a snap-like positive engagement or disengagement therebetween. 